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Bacterial Blast

28 Mar, 2021

Pseudomonas Syringae. Also known as Canker, Bacterial Canker or Gummios.

Bacterial blast is a disease that presents itself by creating open oozing ‘cankers’ on branches or trunks of trees. This causes sudden decay of flower buds and dieback on branches and, in major cases, the entire tree.

Bacterial blast lives on plant surfaces and is spread by splashing water, usually occurring from rainfall. This disease will grow in periods of damp and wet conditions with low temperatures, and in Auckland usually presents itself in autumn to early spring.

Affected branches will slowly die, fail to bud and won’t be able to produce new growth in spring.

Disease development stops when temperatures rise.

Stone fruit trees are the most susceptible to this disease, but the disease can also spread to other trees through open wounds or via the use of a pair of dirty secateurs.


If caught early, bacterial blast can be managed.

If you are pruning plants over winter, always make sure you wait for dry weather. If the cut you make is larger than 1cm, immediately apply pruning paste to help prevent infection.

Take your time in cutting back the tree to create better airflow, especially on stone fruit, as this will lessen the chances of infection. Make sure to disinfect any pruning equipment you use, especially when cutting an affected tree, and get in the practice of following a regular winter spray program.

Certain rootstocks have been known to have better resistance to bacterial canker. Always choose a fruit tree from a garden centre, as stone fruit trees grown from seed are more likely to contract diseases.


If the infection is minor on outer limbs, cut back the diseased wood and remove it from the property (do not use the diseased wood for any type of compost or mulching, remove it immediately).

Apply a copper spray after leaf drop and then again before bud burst.

If the infection has spread to the trunk, you will need to dispose of the tree, as heavily infected plants cannot be treated.

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